In a centrifugal separator of this kind, known for instance through WO 96/12549, it is desired that the stationary housing is only insignificantly larger than the rotor. Thereby, the air resistance to the rotor rotation within the housing can be made as small as possible. Furthermore, within a given space for the whole centrifugal separator the rotor can, thereby, be made as large as possible and, thus, get a capacity as large as possible.
A circumstance making it difficult to have the stationary housing only insignificantly larger than the rotor is that liquid having left the rotor requires a certain space within the housing around the rotor Particularly if the rotor, as in a preferred embodiment of the present invention, is arranged with its rotational axis extending substantially horizontally, the housing can not be made too small. The reason for this is that part of said surrounding wall in this case forms a bottom of the chamber and that liquid, thereby, may collect and form a pool on this bottom, before it runs out through the outlet in the surrounding wall.
The present invention has for its object to avoid the above described difficulty and to make possible that the housing is made only insignificantly larger than the rotor.
This object can be obtained in that the outlet in the surrounding wall is formed in a way such that liquid is allowed to leave the chamber in a direction substantially opposite to the rotational direction of the rotor. An outlet formed in this way creates possibilities for the liquid to rapidly leave the chamber without forming a space-requiring pool therein, which may disturbed the rotation of the rotor. The invention builds on the circumstance that liquid leaving the rotor gets a component of movement in a direction opposite to the rotational direction of the rotor, not only seen in relation to the rotor but also seen in relation to the housing surrounding the rotor.
Thanks to the invention it becomes possible to arrange the centrifugal separator with the rotational axis of its rotor forming an angle with a vertical axis--even extending horizontally--without the housing around the rotor having to be made substantially larger than the rotor. It is particularly suitable to have the rotor outlet situated at one axial end of the rotor and the outlet in the surrounding wall situated at substantially the same axial level in the chamber as the rotor outlet.
For further acceleration of the liquid outflow from the chamber said surrounding wall preferably extends substantially circularly around the rotor and has, at least along part of its extension axially along the rotor, an increasing diameter in a direction towards the outlet in the surrounding wall.